No I don't need more than 192khz (not even that really) nor DSD. The (possible) reason for separate devices would be mostly for Windows WASAPI/DS apps and is as such:
For speakers, my plan is to expand to a 5.1, or maybe 7.1 setup and hook that in to the UCX II. So if I want to listen to something on the speakers, I'll use the UCX's speaker device.
However, for headphones I also like surround sound, but for that you need software to process it. In my case, I use Redscape. It sets up its own virtual audio 8 channel device in Windows (it can actually do ASIO as well). It then convolves the sound for your headphones, and needs somewhere, either ASIO or WASAPI to send it to. That would be where I would use the ADI-2 DAC as the target Redscape sends to.
Basically there's no reason to want to play the convolved audio from Redscape on speakers, and it wants to take exclusive control of the device if it can, so it makes sense to me for it to have its own device it can talk to. Then I just flip the Windows output to whichever device I want to get speakers or headphones.
I suppose there's no particular reason I couldn't have Redscape send to the ASIO inputs of the UCX II and then it send out to the ADI-2 but that seems like extra steps where routing could become messed up if I'm not careful, and it means I have to shut Redscape down when I'm not using it, as it likes to take exclusive control of the device.
I suppose another option would possibly be to use a virtual audio cable, if such a thing exists for ASIO, and then just send all sound to the UCX II, and loop back a surround output from it to Redscape, then back in but that also seems like extra complexity that isn't needed and I imagine I'd need additional software to make it work.
I'm glad to hear the devices will both work on a system together so I can do it how I'm thinking. I'm open to doing it a different way though if there's a good reason. I just have somewhat of a special use case.
Thanks for all the insight and information.